1. Field of the Invention
The present invention relates generally to metal phthalocyanines and more specifically to metal phthalocyanines useful as catalysts and metal interchange sources for curing phthalonitrile prepolymers.
2. Description of the Prior Art
Bis-phthalonitrile resins are known to form thermally stable polymers. Depending on the structure of the prepolymer, however, the resins may be extremely slow in curing to the polymeric state. In general, electron donating groups on the phthalonitrile ring will slow down the cure reaction.
It is not always possible to increase the temperature to accelerate the cure rate because the prepolymer may volatilize or decompose before polymerizing. Further, the higher temperatures result in a less practical processing environment. Currently, a hydrogen source (such as an amine or alcohol) is added to the resin to accelerate or catalyze the cure to more practical times. However, the hydrogen source can present problems; they can partially volatilize during vacuum degassing of the resin and thus change the cure rate and polymer properties. Further, since these accelerators remain in or become a part of the polymer structure, they may compromise the ultimate thermal stability of the system. Finally, the more practical accelerators are aromatic amines which are known to be cancer causing.
Metals may also accelerate the polymerization of bis-phthalonitriles. Because of the higher density of the metals compared to the resin, however, the metals settle out when the resin melts and thus give non-uniform cures and materials.